Chladni Figures

Let's learn a little of physics.
What you see in the image above is named "Chladni figures": "patterns formed by a granular substance on a flat surface vibrating in an own way.
As mechanical waves propagate through an extended object, they do so in all directions. Depending on the characteristic lengths of the body, the boundary conditions that it imposes on the waves can induce the resonance of some of the frequency components of the incident disturbance.
Depending on the vibrational frequency used, you will get one type of drawing or another." (Source: Wikipedia)
Image: at SeCyT 2016. Using differents colour sands, and a type of vibrational frequency, we get the image above.